High frequency stability is a problem in high gain monolithic microwave integrated circuit (MMIC) amplifiers. One common type of high frequency stability problem in microwave amplifiers occurs when input or output impedances of an active device present a negative resistance. This type of stability problem may cause an amplifier to oscillate making the device useless for its intended function. One indicator that a negative resistance type of oscillation may be present is a mathematically derived quantity commonly known as the K-factor. When the K-factor is greater than one, and another mathematical parameter B1 is greater than zero, there is no possibility that the device will present a negative resistance no matter what type of passive source or load impedance the device is presented with. This condition (K&gt;1 and B1&gt;0) is therefore known as unconditional stability.
At higher microwave and millimeter wave frequencies where small parasitic impedances cause drastic changes in the overall load and source impedance, unconditional stability is important for successful MMIC design. Because unconditional stability is required at high frequencies, a traditional method of device stabilization is to use on-chip resistive loading. This will make the device unconditionally stable, but causes severe gain degradation and reduces the overall efficiency of the amplifier. For example, the performance of power amplifiers may be degraded so severely by resistive stabilization, that the devices are not useful as power amplifiers at K-band frequencies.
In addition, the use of higher microwave and millimeter wave frequencies in commercial satellite, mobile communication, and consumer products has fueled the need for high efficiency, low cost MMIC amplifiers. As the need for improved performance at these high frequencies increases, traditional methods of resistively loading the devices for unconditional stability becomes too costly in terms of performance.
Thus what is needed is an unconditionally stable high frequency MMIC amplifier. What is also needed is a high-gain MMIC amplifier where stability is achieved with minimal or no resistive loading. What is also needed is a high frequency MMIC amplifier that provides unconditional stability while improving gain and efficiency without impacting dynamic range of the devices.
What is also needed is a low cost, high gain, high efficiency microwave and millimeter wave frequency power amplifier suitable for use in commercial satellite, mobile communication and consumer products.